ISO 19927:2018

INTERNATIONAL ISO
STANDARD 19927
First edition
2018-08
Fibre-reinforced plastic composites —
Determination of interlaminar
strength and modulus by double beam
shear test
Composites plastiques renforcés de fibres — Détermination de
la résistance interlaminaire et du module par un double essai de
cisaillement de faisceau
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 4
6 Test specimens. 6
6.1 Shape and dimensions . 6
6.1.1 Preferred specimen size . 6
6.1.2 Alternative specimen size . 7
6.2 Preparation of specimens . 7
6.2.1 General. 7
6.2.2 Machining the test specimens . 7
6.3 Checking the test specimens . 7
7 Number of test specimens . 7
8 Conditioning . 7
9 Procedure. 7
9.1 Test conditions . 7
9.2 Specimen dimensions . 8
9.3 Testing speed . 8
9.4 Data collection . 8
9.5 Failure mode acceptance . 8
9.6 Critical load . 8
9.7 Slope of load-displacement curve . 8
10 Calculation and expression of results . 9
10.1 Interlaminar shear strength . 9
10.2 Interlaminar shear modulus .10
11 Precision .11
12 Test report .13
Annex A (informative) Additional details relating to calculation of shear modulus, G .14
Annex B (informative) Interlaboratory study .17
Bibliography .21
Foreword
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 13,
Composites and reinforcement fibres.
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iv © ISO 2018 – All rights reserved

Introduction
Interlaminar shear (ILS) properties of load-bearing composite laminates are important for structural
design, stress analysis and numerical modelling, material development and selection, component
manufacture as well as for repair of delaminated structural components. A number of test methods have
been developed for the determination of shear properties of composite laminates and several have been
1) 1)
standardized, including short beam strength (SBS) [ASTM D2344, ISO 14130, EN 2377 and EN 2563 ],
V-notched beam (known also as Iosipescu shear), ASTM D5379, V-notched rail (ASTM D7078) and
notched tension (ASTM D3846, BS 4994) or notched compression (BS 6464).
SBS methods are very popular due to their simplicity in specimen preparation, test operation and
cost-effectiveness, though they are used to determine only an apparent ILS strength for QA purposes
rather than for use in design. However, a loaded SBS specimen does not have a pure ILS region within its
gauge section so it often fails in a number of modes, dependent on, amongst others, type of composite
materials, lay-up and specimen thickness. Unacceptable SBS failure modes include flexural failure, local
crushing (under central loading roller) and plastic deformation and roller-induced through-thickness
shear band.
The DBS method is based on loading a composite beam on double support spans (i.e. between 5 loading
points), which generates a stress state that minimises axial bending stresses while promoting
interlaminar shear stresses. In DBS tests delamination occurred consistently within one of the pure ILS
regions in the specimens, for a range of laminated composite materials or lay-ups.
Comparisons with the SBS ILS strength results indicated that the DBS ILS strengths were 20 % to >30 %
higher. In addition, a value of the interlaminar shear modulus can be obtained, providing values of E ,
E , G and ν are known or measured separately for the material under test.
22 12 12
1) CEN Aerospace series.
INTERNATIONAL STANDARD ISO 19927:2018(E)
Fibre-reinforced plastic composites — Determination
of interlaminar strength and modulus by double beam
shear test
1 Scope
This document specifies a procedure for determining the interlaminar strength, and modulus, by
double beam shear (DBS) tests of fibre-reinforced plastic composites.
The method is suitable for use with glass or carbon fibre-reinforced plastic composites with thermoset
matrices, providing an acceptable interlaminar failure is obtained.
This document only applies to laminate with a symmetrical and balanced lay-up as it avoids bending/
twisting or bending/extension coupling deformations (see 6.2). The preferred lay-up is unidirectional,
with fibres aligned along the specimen (axial) length.
The suitability of the test for specific lay-ups, matrices and fibres (e.g. natural) are assessed by trial
tests to ensure the correct delamination failures are obtained.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 291, Plastics — Standard atmospheres for conditioning and testing
ISO 472, Plastics — Vocabulary
ISO 1268 (all parts), Fibre-reinforced plastics — Methods of producing test plates
ISO 2602, Statistical interpretation of test results — Estimation of the mean — Confidence interval
ISO 5893, Rubber and plastics test equipment — Tensile, flexural and compression types (constant rate of
traverse) — Specification
ISO 16012, Plastics — Determination of linear dimensions of test specimens
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
critical load
F
crit
load at delamination, as defined in 9.5 for acceptable failure modes
Note 1 to entry: See Cases 1-3.
Note 2 to entry: It is expressed in newtons (N).
3.2
interlaminar shear strength
τ
13 max
shear strength calculated from the critical load
Note 1 to entry: See 10.1.
Note 2 to entry: It is expressed in megapascals (MPa).
3.3
interlaminar shear modulus
G
shear modulus calculated from the slope of the load-displacement curve
Note 1 to entry: See 10.2.
Note 2 to entry: It is expressed in gigapascals (GPa).
3.4
span
L
distance between the outermost support rollers
Note 1 to entry: It is expressed in millimetres (mm).
3.5 Specimen coordinate axes
NOTE 1 The direction parallel with the plate longitudinal axis is the "1" direction and the direction
perpendicular, is the "2" direction (see ISO 1268-4). The direction “3” is perpendicular to the plate (i.e. the
through-thickness direction).
NOTE 2 See Figure 1.
3.5.1
longitudinal tensile modulus
E
tensile modulus in the specimen longitudinal or 1 direction
Note 1 to entry: It is expressed in gigapascals (GPa).
3.5.2
transverse tensile modulus
E
tensile modulus in the perpendicular or 2 direction
Note 1 to entry: It is expressed in gigapascals (GPa).
3.5.3
in-plane shear modulus
G
shear modulus in the 1-2 plane
Note 1 to entry: It is expressed in gigapascals (GPa).
3.5.4
in-plane poisson ratio
ν
Poisson’s ratio in the 1-2 plane
Note 1 to entry: It is dimensionless.
2 © ISO 2018 – All rights reserved

Note 2 to entry: Properties defined in 3.5.1 to 3.5.4 are required for calculation of the interlaminar shear modulus
using either manufacturer’s or measured data (see 10.2).

Key
1 direction parallel with the plate longitudinal axis
2 direction perpendicular with the plate longitudinal axis
3 direction perpendicular to the plate (i.e. the through-thickness direction, with plies layered perpendicular to
this direction)
Figure 1 — Unidirectional reinforced composites plate element showing symmetry axes
4 Principle
A test specimen consisting of a beam of rectangular cross-section is loaded in 5-point flexure, as shown
in Figure 2. The applied load generates regions of pure interlaminar shear stress, as indicated in Figure 2.
The critical load sustained by the specimen when delamination failure occurs is used to determine the
interlaminar shear strength. In addition, the deflection of the specimen under load is used to determine
the interlaminar shear modulus. In order to calculate the interlaminar shear modulus, it is necessary to
know or measure the following properties: E , E , G and ν .
11 22 12 12
Key
1 ILS stress
2 bending stress
a
Load.
b
Sections of pure shear.
c
Support.
d
Displacement measurement points.
Figure 2 — Stress distributions in DBS specimen
5 Apparatus
5.1 Test machine
5.1.1 General
The test machine conforms to ISO 5893 as appropriate to the requirements given in 5.1.2 to 5.1.3.
5.1.2 Speed of testing, v
It shall be kept constant according to ISO 5893.
5.1.3 Indicator for load
The error in the indicated force is less than ±1 % of the load to be measured (see Class 1 of ISO 7500-1).
5.2 Micrometer or equivalent, capable of reading to 0,01 mm, or less, and suitable for measuring the
thickness, h and width, b of the test specimen. The micrometer shall have faces appropriate to the surface
being measured (i.e. flat faces for flat, polished surfaces and hemispherical faces for irregular surfaces).
4 © ISO 2018 – All rights reserved

5.3 Loading fixture, a 5 point flexure jig with adjustable spans, as shown schematically in Figure 3.
The loading/support rollers are uniformly positioned within the span (tolerance ± 0,2 mm), as shown in
Figure 4. The loading/support rollers have a contact diameter of 6 mm (tolerance 0 mm to –0,1 mm). A
typical set-up is shown in Figure 5.
Key
1 loading rollers
2 support rollers
3 specimen
Figure 3 — Schematic of double-beam shear fixture
a) Side elevation b) End elevation
Key
1 loading points 6 inner region
2 support points 7 specimen thickness
3 span 8 specimen width
4 1/2 span 9 specimen length
5 outer region 10 Fibre direction (unidirectional specimen)
Figure 4 — Test specimen and rollers lay-out for determination of interlaminar modulus and
strength
Key
1 interlaminar crack
Figure 5 — Test specimen mounted in double-beam shear fixture used for strength and
modulus determination
5.4 Displacement measurement
A suitable displacement transducer (e.g. a DVRT-type of LVDT or single arm extensometer) is used
to measure the deflection of the specimen at the mid-point of the inner span (i.e. 0,375 L from an
outer support position). The equipment shall be calibrated for displacement. The unit should record
continuously the displacement of the lower surface of the specimen to ±1 % of the displacement to be
measured (i.e. Class 1 of ISO 9513). The displacement measurement equipment shall be calibrated and
traceable.
6 Test specimens
6.1 Shape and dimensions
6.1.1 Preferred specimen size
Specimen A shall have a width, b, of 10 mm ± 0,2 mm, a thickness, h, of 2 mm ± 0,1 mm and a length, l, of
30 mm. This is the same cross-section as used in ISO 14130.
Specimen B
...